Diuretics are drugs which increase the amount of fluid excreted by the kidneys. They do this by inhibiting the re-absorption of water in the kidney.
Diuretics are used by sportsmen and women to decrease body weight, to increase power to weight ratios and to help qualify for certain weight catagories, eg boxing and judo. By taking diuretics, the athletes run the risk of severe dehydration and even gout. Other side effects include potassium defeciency, leading to muscle cramps, if a potassium sparing diuretic isn't used.
The azide group of diuretics, these aren't potassium sparing diuretics.
(NB the bracketed names are the drugs' commercial names.)